The invention relates broadly to panels or structural members designed to dissipate, isolate or reduce noise caused by acoustic wave energy. More specifically, the present invention relates to acoustical panels designed to reduce industrial noise generated by industrial machinery.
Acoustical panels heretofore utilized in varying degrees reflectance, interference, and/or absorption of acoustical wave energy to isolate or dissipate acoustic noise. U.S. Pat. No. 1,611,483 to Newsom illustrates sound intercepting panels which reflect objectionable noises away from an open window. At FIG. 10 of the Newsom patent, a certain amount of acoustical wave interference is illustrated. However, it appears that a major portion of the noise reduction in Newsom is accomplished by the reflection. An acoustical panel or sound intercepter which relies primarily upon the reflectance of acoustical wave energy has the disadvantage of not dissipating the acoustical wave energy, but rather merely redirecting the acoustical wave energy to another location. Of course, a certain amount of dissipation occurs merely through the transmission of the acoustical wave energy over a distance and also through the mass or isolative characteristic of the reflecting material.
U.S. Pat. No. 2,057,071 to Stranahan illustrates a sound insulating panel which utilizes the mass or isolative characteristic of a portion of the panel material and also the resistive absorption characteristic of another portion of the panel material. In Stranahan, the mass or isolative characteristic of the panel is enhanced by utilizing a heavy metal foil, such as lead foil, as outer layers of a soundproofing material. The resistive absorption is accomplished in Stranahan by utilizing an acoustic absorbing material such as felt sandwiched between the outer layers of lead foil. To increase the sound insulating capabilities of the Stranahan panel, either the mass of the lead foil is increased or the thickness of the felt is increased. Stranahan illustrates the typical drawbacks of sound insulating panels which utilize the mass characteristics or resistive absorption characteristics of material to accomplish sound insulation. That is, in order to increase the sound insulation capability of the panels, the mass or size of the panels must be increased. Hence, the panels may become either excessively heavy or excessively large.